This relates to packaged semiconductors and more particularly to packaged integrated circuits with encapsulants.
When packaging integrated circuits in a plastic ball grid array (PBGA) a mold filling process is typically performed to encapsulate the integrated circuit in order to protect the device from environmental damage. To perform the encapsulation, a cavity is placed over a semiconductor die, which is over a packaging substrate, and an encapsulant material is flowed over the semiconductor die and under the cavity. However, this process often results in the encapsulant flowing outside the area under the cavity (bleeding) due to a gap between the package substrate and the bottom edge of the cavity caused by the presence of traces (metal lines) on the package substrate. This bleeding decreases the quality of the resulting package and can potentially be a reliability issue for the package and the encapsulation equipment. In addition, the bleeding is aesthetically undesirable. Thus, additional subsequent cleaning process steps to remove the bleeded material from the package substrate and the encapsulation equipment are performed.
One way to mitigate bleeding is to apply a large pressure to the top and bottom surfaces of the semiconductor package so that the size of the gap between the package substrate and the cavity is minimized. This large pressure results in cracking of the solder resist, which is a protective layer formed over the integrated circuit and traces. Solder resist cracking can result in decreased reliability of the device by making the package substrate prone to corrosion, for example.
In order to decrease solder resist cracking and allow for a large pressure to be applied during encapsulant formation, dummy traces 10 have been formed on a package substrate 5, as shown in FIG. 1. Bond pads 30 on an integrated circuit 20 are connected to electrical traces 50 by wire bonds 40 and bond fingers 45. The electrical traces 50 include a bond connection 12, a signal portion 15 and a plating portion 17. The dummy traces 10 are orthogonal to an edge of the package substrate 5 and/or parallel to the plating portion 17. The dummy traces 10 are not electrically connected to the integrated circuit 20. One problem with using dummy traces 10 is that they are not sufficient for preventing fine filler encapsulant material from bleeding, which is being used as the industry moves to fine pitch wire bonding, meaning the distance between the bond pads 30 is decreased to less than approximately 60 microns. For fine pitch wire bonding, smaller filler is needed in the encapsulant material to reduce wire sweep. (Wire sweep is the touching or shorting of adjacent wires.) Gaps between the encapsulant dummy traces 10 are not sufficient for blocking particles, especially those used in fine filler encapsulant materials. Therefore, a need exists in order to prevent bleeding when using fine filler material for fine pitch packages.